There are so many roles within OCS that it can be overwhelming if you don’t know where to start.
I recommend starting with the Front-End server, then proceeding to the Edge, followed by CWA, Mediation, Monitoring, and then Archiving.

Microsoft has made the process easier with a new Update Resource Center http://technet.microsoft.com/en-us/office/ocs/ee695846.aspx, and a Cumulative Server Update Installer KB 968802 (released 11/9/09) that detects the role and then applies only the appropriate hotfixes to the role.
The only thing this tool is missing is it does not install the Database hotfix KB 969834. The database hotfix must be applied after the Update Installer finishes, otherwise the Conferencing Attendant service will not accept attempts to start conference calls from remote attendees (the userpin service fails to connect to the database, because the schema is not what the binary expects).
One of the gotcha’s with this tool is it does not prompt to restart the Mediation server services, whereas the other roles prompt you to restart the server. This causes a problem because
you’re left to assume that a restart is not necessary. The services continue to run fine. However, before mediation can hand off calls to the front end, you need to at least restart the mediation service (or simply reboot).

As always, before applying patches, verify that you have backups, and that you have recently tested a restore to an alternate DR environment.
It should go without saying, but testing all components of OCS is also important. Here is a sample test plan to use after applying updates:

1) Call the Conference Attendant
2) Call Outlook Voice Access
3) Call a number tied to each location profile/mediation server
4) Schedule a live meeting and test audio/video externally and internally
5) Test federation
6) Test Communicator Web Access

There are a few suprises after this latest round of OCS patching.

But it doesn’t let you change it. The field becomes populated if you use the ext structure in your tel URI. So, for example, if your number was +12045551212;ext=1212 the 1212 extension would be listed on the CWA page.